Make UseSingleQuote compliant with the YAML spec (#647)

* Make UseSingleQuote compliant with the YAML spec

* Make it self-explanatory

encode_test.go

@@ -704,7 +704,7 @@ func TestEncoder(t *testing.T) {
 		},
 		// Quote style
 		{
-			`v: '\'a\'b'` + "\n",
+			`v: '''a''b'` + "\n",
 			map[string]string{"v": `'a'b`},
 			[]yaml.EncodeOption{
 				yaml.UseSingleQuote(true),
@@ -717,6 +717,13 @@ func TestEncoder(t *testing.T) {
 				yaml.UseSingleQuote(false),
 			},
 		},
+		{
+			`a: '\.yaml'` + "\n",
+			map[string]string{"a": `\.yaml`},
+			[]yaml.EncodeOption{
+				yaml.UseSingleQuote(true),
+			},
+		},
 	}
 	for _, test := range tests {
 		t.Run(test.source, func(t *testing.T) {

stdlib_quote.go

@@ -53,8 +53,18 @@ func appendQuotedWith(buf []byte, s string, quote byte) []byte {
 
 func appendEscapedRune(buf []byte, r rune, quote byte) []byte {
 	var runeTmp [utf8.UTFMax]byte
-	if r == rune(quote) || r == '\\' { // always backslashed
-		buf = append(buf, '\\')
+	// goccy/go-yaml patch on top of the standard library's appendEscapedRune function.
+	//
+	// We use this to implement the YAML single-quoted string, where the only escape sequence is '', which represents a single quote.
+	// The below snippet from the standard library is for escaping e.g. \ with \\, which is not what we want for the single-quoted string.
+	//
+	// if r == rune(quote) || r == '\\' { // always backslashed
+	// 	buf = append(buf, '\\')
+	// 	buf = append(buf, byte(r))
+	// 	return buf
+	// }
+	if r == rune(quote) {
+		buf = append(buf, byte(r))
 		buf = append(buf, byte(r))
 		return buf
 	}